The present invention relates to an organopolysilazane and, more particularly, to organopolysilazane compositions containing free radical generators that can be crosslinked by an energy input.
Organopolysilazanes are well-known products that occur in the form of monomers, oligomers, ring or linear polymers, and resinous polymers. These organopolysilazanes can be prepared using a wide variety of methods from a wide range of starting materials.
These organopolysilazanes can be, in particular, shaped and pyrolyzed in the form of Si.sub.3 N.sub.4, SiC or their mixtures. The silicon nitride can be manufactured by reacting chlorosilanes (SiCl.sub.4, HSiCl.sub.3 and H.sub.2 SiCl.sub.2) with ammonia at a high temperature and in a vapour phase. It is difficult to manufacture shaped articles, especially fibers, using this method, since the method directly yields a powdered product. In contrast, organopolysilazanes can also be spun into continuous fibers which upon pyrolysis yield ceramic fibers.
Organopolysilazanes can be shaped into films of various gauges and into massive molded articles. The organopolysilazanes can be used as binders for ceramic fibers or carbon fibers. The organopolysilazanes can also be used as sintering binders for porous ceramic articles. However, difficulties are encountered in converting these organopolysilazanes readily and economically into the form of fibers or coatings that, after pyrolysis, yield ceramic products in the form of fibers, films, coatings of various gauges and molded articles.
An attempt to provide a solution to these problems was made in U.S. Pat. No. 3,853,567. According to this patent, a process is proposed for the manufacture of shaped articles, such as fibers comprising silicon carbide, silicon nitride or mixtures thereof, with other ceramic products, by first carrying out the thermal treatment of an organopolysilazane at a temperature between 200.degree. C. and 800.degree. C. The process obtains a meltable carbosilazane resin that can be melt-spun and then pyrolyzed at a temperature between 800.degree. C. and 2,000.degree. C.
The above patent certainly represents a significant step forward, but it has two disadvantages. First, it requires thermal treatment at a temperature that is very high, namely 200.degree. C.-800 .degree. C. Secondly, the process requires a carbosilazane in melt form under anhydrous conditions and in an inert atmosphere. In addition, the weight yield of the ceramic can be inadequate.
Japanese Patent Application Kokai No. 77/160,446 describes a process for the polymerization of organopolysilazanes of high molecular weight by using acidic earths as catalysts for the treatment of organopolysilazanes. However, this process has the major disadvantage of requiring the solid catalyst to be separated off by filtration. This implies the use of a solvent in the case of polymers having high viscosities.